In an Ethernet (registered trademark) network, a ring shape topology of a plurality of repeaters, i.e., Ethernet switches, or simply switches, are arranged by connecting those repeaters in a ring/circuit shape. In such a ring shape topology of the repeaters, or the switches, two ports of one switch are connected to ports of two other switches, for a ring shape topology/arrangement of the network. Thus, two communication routes are established between the two switches, one communication route along a clockwise direction of the ring shape network and the other communication route along a counter-clockwise direction.
More practically, the following situation clarifies the above description. That is, when one switch has at least four ports, among which two ports are ring ports for a ring connection of the switches, and the other two ports are normal ports that are respectively connected to two devices (e.g., to a device A from a switch 1 and to a device B from a switch 2), one data communication frame transmitted from the device A reaches the device B in either of the two communication routes described above, because (A) the transmitted frame from the device A may come in from one normal port of the switch 1 to go out from one ring port of the switch 1 to take a clockwise route to reach the switch 2 and to go out from one normal port to the device B, or (B) the transmitted frame from the device A may come in from one normal port of the switch 1 to go out from the other ring port of the switch 1 to take a counter-clockwise route to reach the switch 2 and to go out from the same normal port to the device B.
On the other hand, a patent document 1, JP 2010-509825 A, (Patent document 1) discloses an idea of transferring the frame in a predetermined shortest route to the destination, i.e., from one node to the other node.
The situation described in the above is further examined in terms of how a frame transfer from one device to the other is improved when one switch in the ring shape topology receives a frame that is addressed to a device connected to the normal port of the other switch. That is, how to efficiently transfer a data communication frame from one device connected to the normal port of one switch to the other device connected to the normal port of the other switch is discussed in the following. The data communication frame in question may also be designated as a “frame to other-switch-hung device”.
Apparently, in the above-described situation, the network traffic increases more than required when, after the reception of the “frame to other-switch-hung device” in one switch, one switch transmits the two frames from the two ring ports onto the ring-shape network, because one of the two frames that are respectively transmitted from the two ring ports may be dispensable.
On the other hand, when the switch is configured to transmit the frame from only one of the two ring ports onto the ring-shape network after the reception of the “frame to other-switch-hung device”, the increase of the network traffic may be prevented. However, the communication route to the other-switch-hung device” may not be the shortest one. Note that, in the patent document 1, an idea of shortest route transmission of the frame is disclosed without describing a concrete method for realizing/implementing the idea.